This study will evaluate the effects of low magnitude, high frequency stimulus on bone mineral content(BMC), bone mineral density (BMD), and bone strength in childhood cancer survivors who present with BMD values 1.0 or more standard deviations below the mean for their age and gender for the lumbar or whole body. This study will evaluate the effects of low magnitude, high frequency stimulus on markers of bone turnover in childhood cancer survivors who present with BMD values 1.0 or more standard deviations below the mean for their age and gender for the lumbar or whole body.